Despite the growing importance of research concerned with cognitive issue in financial markets and the historical process of their development (Carruthers and Stinchcombe 1999, Muniesa 2007) they have not been interested in the hierarchy of knowledge. Building, on the structural approach (Lazega 1992, 2009) we evidences the role of central actors in this hierarchization. They try to make the positive knowledge visible while hiding negative information. Our study of the Exchange Traded Funds market in France is based on a methodological process as follows: First, the definition of knowledge relayed by various written supports including: academic papers in Finance, reports from different institutions and press articles. Then, ranking those written supports by the 57 actors interviewed. Finally, explaining the hierarchy of knowledge by analyzing the network of information exchange. Our analysis suggests the predominance of knowledge that reflects the market development and the positive attributes of ETFs while the theme of risk is kept in the margin. This is explained by the centrality of managers and marketing officers from banks in the network of information exchange which allows them to retreat the expert information of traders and exert social control over journalists. Furthermore, the existence of a social niche of banks and two intermediaries facilitates cooperation between competing issuers that encourages the dissemination of this positive knowledge.